Lens mount



Dec. 16, 1941. RU WE 2,266,16Q

LENS MOUNT Filed July 25, 1959' 2 Sheets-Sheet 2 I 52 59 55 62 63 56 5/ 57 w W \W 65 1 WM 3 I P A TTORNE Y INVENTOR W/W Patented Dec. 16, 1941 Chester W. Crumrine, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y.,

a corporation of New Jersey Application July 25, 1939, Serial No. 286,384

4 Claims.

T is invention e at s to pt cal s stem and art ula y to en m un siit is the object of the present invention to provide an inexpensive method and means for mounting lenses and particularly lens elements or simple achromats.

Due to variations in any lens manufacturing process, particularly the less expensive processes such as molding, all lenses of the same design are not identical and a large batch of lenses will include some samples whose power will vary as much as 2 per cent or even more from the predicted value. The variations in power may be due to variations in thickness, variations in refractive index, or more rarely variations in surface curvatures. When the lens is to be used alone (e. g. a simple meniscus lens) these vari ations are compensated for by measuring or otherwise determining the focal length of the lens and adjusting it in its mount, usually by using shims, so that the lens is positioned in front of the desired image frame (the film plane in a camera) a distance equal to its back focus distance. In fixed focus cameras, the back focus distance is usually conjugate to about 25 feet object distance, i. e. is almost equal to the bacl; focal length.

It is the primary object of the present invention to provide a mount for a lens which is inexpensive and which in itself compensates for any variation of the power of the lens from its correct or predicted value.

' With lenses according to the invention, the camera manufacturer or the manufacturer of complete optical systems including the mount can safely assume that as far as his work is concerned, the lenses all have the same focal length and will be accurately focused without any special care to distinguish between the different lenses of the batch.

According to the invention variations in focal length may be compensated for by determining the back focus distance of each lens and molding a plastic rim onto the periphery of the lens with one end surface ofthe rim a fixed distance from its back focus. The .rim on the lens will have inner and outer surfaces and front and rear surfaces the latter two being end surfaces. The invention as thus applied insures that the lens will be the correct distance from the desired image plane independent of its focal length, provided the adjusted end surface of its rim is a predetermined fixed distance from this image plane.

Furthermore, one embodiment of the invention finds more general application, namely for mounting lenses in more complicated lens systems such as used as anastigmatic photographic lenses. In this case, the individual components (elements or cemented lenses) are more carefully made and the variations from predicted power values are small and mainly due to errors in thickness of the element. However, the exact positioning of these lenses relative to the Other lenses and to the film plane is more critical and requires more than just insuring that the back focus is correct. As is well known, slight changes in the spacing of the lenses in a complex system, change the aberrations, particularly distortion and curvature of field. When applying the present invention to a complex case, the spacing of the front and rear surfaces of the rim for each lens from that lens with respect to the power of that lens is determined. After that the separate lenses are all inserted in a mount with their rims against separate abutments or against one another. The first alternative permits positioning each lens separately with respect to the image plane and the second alternative permits positioning them relative to one another which is, of course, preferable.

In both embodiments (the single lens and the complex lens system) the end surfaces of the lens rim are spaced from the lens in accordance with the focal length of the lens or at least in accordance with some factor such as the lens thickness which determines the focal length thereof. The relationship is a simple direct one only in the case of a single lens system, i. e. an increase of 1 mm. in the focal length requires an increase .or decrease of 1 mm. in the spacing of the end surface of the rim. Elements of complex systems are adjusted for minimum aberration and the relationship follows the complex mathematical laws discovered by lens designers.

According to the preferred embodiment of the invention, such a mount is produced by using a molding machine which includes a concentric lens hold ng device and an adjusting screw for moving the lens and lens holding device toward or away from the surface of the mold which forms the end surface of the rim. The lens and/or the rim may, of course, be circular, rectangular or any desired peripheral shape. The adjusting screw r whatever equivalent is used for moving the lens holding means relative to the rest of the mold in accordance with the focal length of the lens is provided with and constitutes part of the mold. A scale to be manually set may be coupled to the adjusting device to indicate the setting thereof in terms of lens focal length. On the other hand, if the only variable which is present to cause variable focal length is variable thickness, the lens holding means may be adjusted in accordance with this thickness as by a clamp or rider touching the lens itself. This invention is particularly useful along with those described in copending applications, Serial Numbers 286,385 and 286,386 filed concurrently herewith by myself and by Donald L. Wood respectively.

Other objects and advantages of the invention Fig. 2 shows a molding machine according to one embodiment of the present invention.

Fig. 3 shows the adjustment scale of the device shown in Fig. 2.

Fig. 4 shows the lens element of Figl-mounted according to the invention.

Fig. 5 shows a camera having a lens mou according to the invention.

Fig. 6 shows a Cooke type lens mounted 'ac,-' cording to the invention, Y

Fig. 7 is a horizontal cross section of a mold according to the invention for mounting a view finder system. i

Fig. 8 is a view finder system mounted by the apparatus shown in Fig. 7.

Fig. 9 is an end elevation of the view finder shown in Fig. 8. w In Fig.1 there is shown an ordinary meniscus lens element Iii having an optic axis ii and an axial thickness t. This is a meniscus lens with itsufront and rear curvatures R2 and Rt respectively. This figure represents one of a large number of lenses as normally produced by any of the common manufacturing processes. As is well'known, lenses of a particular batch vary from one another. For example the lens may not be centered and the diameter measured from the optic axis H may be different, as shown by HI and H2. The present invention is concerned with other variations such as variations in thickness t or variations in the curvatures Bi and R2 or even variations in the index of refraction of the glass used. These variations cause a'variation in focal length'or power of the element and it is customary when using such lenses to measure their focal length and to mount them in a camera accordingly. The usual procedure is to sort the lenses into batches according to focal length and then to mount all of the lenses of one batch in the same way. When changing, to another batch of lenses the camera is adjusted accordingly. 7 In Fig. 2 there is shown the cross section of a simplified molding machine for mounting the element shown in Fig. 1 so as to compensate for these variations in focal length. The molding dies comprise an uppermold IE which may be heldin any suitable manner against a lower mold ll. The. lens element in is-carried byplungers I2 and I3 mounted in the molds l6 and I! respectively. For centering the lens, the plungers l2 and I3 are provided with a zonal clamp consisting of members M and I5 respectivelywhich clamp members separate the peripheral chamber 26 from the paraxial chamber 28. The arrangement shown is an injection molding machine ted and, the plastic is injected through a nozzle 21 into the chamber 26 and forms a plastic rim on the lens; which rim '3! is best seen in Fig. 4. The

zonal clamp members i l and I5 prevent the plastic from' reaching the chamber 28. Furthermore'since the clamp member l4 has a diameter equal or less than that of the clamp member l5, there is no upward component of the pressure under which the plastic is injected against the plunger I2. I t

The plunger I2 is held down against the lens Ill by means of a spring l9 and rigid plate 20. The plunger l3 is held up against the lens I!) by means of a screw 2| on rigid plate 22.

According to the invention, this screw 2! is clamp member l4 upward against the force of the spring [9. This moves the lens l0 nearer to the lower wall of the mold I6, i. e. nearer to the upper wallof the chamber 26.

As seen in Fig. 4 this movement reduces the distance d-between the end surface of the rim 3| and the lens Ill. The distance d is measured on the optic axis H of the lens H). In the example shown, the lens It is supposed to have a focal length of 50.0 mm. That is, the averagefocal length of a large batch oithese lenses is 50.0mm. Due to manufacturing errors these lenses may vary as muchas 2 per cent i. e. anywhere from 49.0 mm. to 51.0 mm. When practicing the pies ent invention, the lenses are all sorted according to focal length and the rims Mare molded onto one batch at a time. The scale "24 isadju sted to the focal length of the batchto be run and all of the lenses of this batch are moun ted without changing this adjustment, The adjustment is then changed in accordance with the focal length of another batchand this other batch is then run off, the lenses are delivered to the camera manufacturerwho is then free to consider that all of the lenses have exactly the same focal length. This is due'to the fact that the camera manufacturer mounts the lens in accordance with the endsurface of the rin i SII Thus there is eliminated all adjustments of the lens mount of the camera which adjustment ordinarily involves grinding'or the use of shimsf f The lens [0 inits lens mount 3lis shown in Fig. 5 as mounted in a 'camera'BZ'. 'The camera 32 is of molded construction and has a fi lm plane 34 andopposite to it a recess" in the housing 32 which recess is shaped accurately to receive the lens l0 and its rim 3i. The diaphragm 35 of the lens H] is molded into the camera housing 32. When the lens ill in itsim ount 3| is inserted in the camera 32 so that the rear end surface of the mount 3! presses against'an abu tment 33 in the camera 32, the lens is properly focused with respect to the film plane 34 This is a fixed focus camera and hence the back focus, 1. e. the distance between the lens ii! and the film plane 34should be slightly greater than the focal length of this lens II] and equal to thefocus conjugate to an object distance of about 25 feet. That is, the back focus of the lens is should equal the distance 1+d. In the manufactureof the cameras the distance 1 is maintained constant and this procedure is perfectly satisfactory since the distance d is preadjusted according to thefinvention in accordance with the focal length of the lens element Ill r i Thus according to theinvention by merely inserting the element I0 manually into the camera 32 so that it presses against the abutment 33, one is able to perform theform'erlyexpensive operation of focusing the lens. Furthermore since the lens is also mounted in accordance with the invention of Wood as described in his above-mentioned application, this same simple operation automatically centers the lens ID on the optic axis of the camera 32 which was also an expensive operation formerly.

In Fig. 6; a complex photographic objective comprising spaced elements '40, 4|, and 42 is mounted in accordance with the invention. Each element is'mounted according to'theinvention in a rim 44, 45, and 46 respectively with both end surfaces of the rims adjusted with respect to the focal length of the elements 40, 4|, and 42 respectively so that when these elements are inserted in a lens mount 43 as shown, the elements are properly adjusted to have the minimum distortion. That is, the lens system is computed so as to have a minimum amount of aberrations and then any slight variations of the elements 40, 4| and 42 from their correct values are compensated for by adjustment of the individual mounts f the elements during molding. The end surface of the element 46 is against an abutment 41 in the mount 43 and the end surfaces of the other rims 45 and 44 are in contact successively. A ring 48 mounted in a screw thread in the mount 43 holds the rim 44 against the rim 45 and the rim 45 against the rim 46. That is, the elements have thickness d8, 035, and d2 respectively and the spacing of ,these lenses from the end surfaces of rims, which spacings are labeled dl, d3, d4, d6, (Z1, and (19 are adjusted in accordance with the invention. It will be noticed that d9 is actually negative with respect to the other spacings but is, of course not critical. dl may determine the back focus of the system or this may be separately adjusted in which case dl is not critical either. d3, d4, dB and d! are adjusted so that the separation of the elements 40, 4| and 42 are such that aberrations are a minimum.

In Fig. 7, a method of mounting a view finder according to the invention is illustrated. This figure illustrates only the lower half 53 of a molding machine and no injection nozzle appears in this cross section. Fig. 7 is perhaps best understood by reference to Fig. 8 which illustrates the resulting optical system. The lenses and 52 are held in correct optical alignment and correct- 1y spaced by zonal clamps 54, 55, 56, and 51 and while in this position a housing for the view finder and a mount for each element is molded all of one piece. This housing and mount is illustrated in Fig. 8 as 50. By means of screws 64 mounted in plates 65, the zonal clamp members 54 and 51 are adjusted axially. The zonal clamp members 55 and 56 are held by springs 59 mounted in pistons 66 which are adjusted by rods 6| pivoted at the point 62.

The operation of this device is as follows.

Screws 64 are adjusted in accordance with the focal lengths of the elements 52 and 5|. The elements 52 and 5| are then inserted in place and the connecting rods 6| are turned on the pivot 62, the amount of turning being determined by abutments 63 to bring the clamps 55 and 56 against the elements 52 and 5| respectively. The plastic to form the mount 50 is then injected and allowed to harden. The pressure of the clamps 55 and 56 is then released by turning the rod 6| clockwise and the whole inside portion of the mount including the clamp members 55 and 56 and the cylinder in which these clamp members slide is removed with the upper portion (not shown) of the mold. In the arrangement shown, it would then be necessary to move the clamp members 54 and 51 outward so that the lens mount 50 could be removed from the mold. Any convenient and quick method for moving the clamp members 54 and 51 together with the screws 64 and plate 65 may be employed in this connection or the screws 64 may be unscrewed the necessary distance.

In molding view finder systems as shown in Figs. 7 and 8, only three sides of the housing are formed in this mold and the fourth side or cover is molded. separately. This is best seen in Fig. 9 which illustrates the end view of the view finder system shown in Fig. 8. In the arrangement shown the view finder housing 50 has an end surface 10 and a bevel adjacent to the lens element 5|. The upper surface or cover of the view finder is formed by a molded fiat plate 12 having projections -'|3 thereon corresponding to the projections from the housing 50 which form the mounts for the lenses 5| and 52. In general the cover 12 is not necessary since the view finder is mounted on a camera which is itself properly molded to act as the fourth surface of the housing 50.

Because of the complexity of the mold, view finder systems are generally molded individually but of course it is possible to mold several simultaneously as is customary in the molding art. Of course, the molding of the rim 3| for the lens elements ID as shown in Figs. 1 to 4 is usually carried out so that 8 or 10 lens rims are molded simultaneously on a star mold.

Having thus described the various embodiments of my invention, I wish to point out that it is not limited to the specific structures shown but is of the scope of the appended claims.

What I claim and desire to secure by Letters Patent of the United States is:

1. A device for mounting a lens to compensate for any variation in the rear focus thereof from the correct value which comprises means for molding a rim onto the periphery of the lens, said molding means including a mold surface for forming one of the end surfaces of said rim, means for holding the lens in the molding means at a predetermined distance from said mold surface during the molding and adjusting means on the molding means for adjusting said predetermined distance before the molding to bring said one of the end surfaces of said rim to a fixed distance from said rear focus.

2. A device according to claim 1 in which said lens holding means centers the optic axis of the lens with respect to the periphery of the rim mold.

3. A device for molding a plastic rim onto a lens element comprising means for receiving and holding the plastic during molding which plastic molding means includes walls for defining the outer periphery of the rim, walls for defining the end surfaces of the rims, and lens holding means for defining the inner surface of the rim and for holding said lens element and means for adjusting the lens holding means relative to the walls defining the end surfaces of the rim in accordance with the power of the lens element.

4. A device for mounting an optical system including a plurality of spaced elements, which device comprises means for molding in one piece a plastic housing for the system and rims gripping the peripheries of the elements and extending at least partially there-around, means forming part of said molding means for holding the lens elements in optical alignment in the housing during molding and means for axially adjusting said holding means in accordance with the powers of the elements to compensate for slight variations of said powers from their correct values.

CHESTER W. CRUMRINE. 

